Fungal mycelia show lag time before re‐growth on endogenous carbon

Abstract

Nutrient starvation is a common occurrence for filamentous fungi. To better understand the effects of starvation, we used a parallel plate flow chamber to study individual fungal mycelia when subjected to a step change in glucose concentration. We report the presence of a finite "lag time" in starved mycelia during which they ceased to grow/extend while switching from growth on exogenous carbon to re-growth on endogenous carbon. This lag time precedes other morphological or physiological changes such as change in growth rate (50-70% reduction), vacuolation (up to 16%), and decreased hyphal diameter (almost 50% reduction). Data suggests that during lag time, vacuolar degradation produces sufficient endogenous carbon to support survival and restart hyphal extension. Lag time is inversely related to the size of the mycelium at the time of starvation, which suggests a critical flow of endogenous carbon to the apical tip. We present a mathematical model consistent with our experimental observations that relate lag time, area, and flow of endogenous carbon.

The carbon starvation response of Aspergillus niger during submerged cultivation: Insights from the transcriptome and secretome

“…Similar to our results, morphological data from A. oryzae [25] indicate a sharp transition between thick and thin compartments (Figure 2B) in response to carbon starvation, suggesting that hyphal diameters can be used to distinguish populations of old and young hyphae formed during primary growth on the supplied carbon source and secondary growth fueled by carbon recycling, respectively. To visualize the transition dynamics from thick (old) to thin (young) hyphae in response to carbon starvation, an image analysis algorithm was developed to analyze hyphal diameter distributions of the cytoplasm filled mycelial fraction.…”

“…In flow chamber experiments with A. oryzae , Pollack et al [25] followed single hyphae and studied their response to glucose depletion. Similar to our results, they observed secondary growth fueled by carbon recycling, which was morphologically characterized by the formation of hyphae with significantly reduced diameters.…”

Autophagy in filamentous fungi

“…In filamentous fungi, autophagy is typically accompanied by vacuolar enlargement. Vacuoles are degradative organelles, and hyphal vacuolation has been shown to increase rapidly in nutrient-starved Aspergillus oryzae mycelia (Pollack et al, 2008). Autophagic bodies are found inside vacuoles when autophagy is induced, but not in mutant strains defective of autophagy, such as in the A. fumigatus DAfatg1 strain (Richie et al, 2007).…”

Autophagy in Plant Pathogenic Fungi

“…Hyphal vacuolation has been shown to increase rapidly in nutrientstarved Aspergillus oryzae mycelia [33]. It has been demonstrated that autophagic bodies can be visualized in vacuoles under starvation conditions; however, autophagic bodies cannot be detected in autophagy-blocked mutants, such as in the A. fumigatus ΔAfatg1 mutant or in the M. oryzae ΔMoatg1, 4, 5, and 9 mutants [5,31,[34][35][36].…”